Is it in the ground or in a pot? If in a pot did you keep it well watered when we had the very hot spell last year? Alternatively it is in an exposed windy position which they don't like.

It's in the ground and was well watered last summer but is exposed to the wind, I have heard that they can get leaf burn but not that it can kill the tree, thanks for your reply.

It's in the ground and was well watered last summer but is exposed to the wind, I have heard that they can get leaf burn but not that it can kill the tree, thanks for your reply.

Did you prune it at all because they hate being cut back. Mine took a couple of years to get over the "trim" I gave it.

If the part that;s died back is on the side which gets the wind, it'll be that.

if the acer is not too exposed, it could also be Verticillium wilt, this affects branches individually by closing them down as it starts at the roots and the tree goes into survival mode.

I had the same problem with my Acer 4 or 5 years of age. The leaves started to dry up and drop off and branches started to die. I took a sample of the dying branch to my local nursery man he suggested that the sap flow was being restricted by a disease. He told me to trim all of the dead and dying wood back and watch it grow. The Acer fully recovered and looks healthier now than before the problem.